8.9/10 from me
It could change later, I don't know for sure. It's an event, ambitious, heart-breaking and emotionally throughout but there are some things that prevent me to give it more than 9/10. I think one of them is that the Russos are not on that level yet to juggle this giant story perfectly. Overstuffed, I may say.
Thanos is great. One of the best MCU has to offer (I have to let it settle for a few days before deciding if he's the best MCU villain or not). Here's the thing, in his eyes his mission is noble and you can see why. I'm kinda disappointed with Black Order, however.
Also, Thor is amazing. He's now my favorite avenger after Cap.
With all that said, this film is worth the hype. It's huge and it's a worthy culmination of everything that MCU built until today. Although I think I like Ragnarok a bit more.